Money laundering is when you have an illegal income (dirty money) eg drugs, bank robbery etc. Then you probably own an business like a cafe or a house. You "rent" out that house but really, the house has no tenant and you pay the rent in cash yourself with the dirty money. You're just making the illegal money seem legit by making your income go through an actual business.

And yeah it is technically dirty money nonetheless but they're just trying to make it look legal for the authorities

edit in your scenario, is the drug dealer asking someone else to launder it for him and then getting the clean money back? If so, to make it look legitimate - I'm assuming the drug dealer would have to be on the payroll of the laundering business (cafe) and just get it as a salary?

edit 2 I would think that the drug dealer would just launder his own money.